1. Field of the Invention
The present invention relates to an apparatus capable of heating or cooling a polishing surface of a polishing pad or fixed abrasive of a polishing apparatus for use in polishing various workpiece, such as a semiconductor wafer, various types of hard disk, a glass substrate, a liquid crystal panel, or the like.
2. Description of the Related Art
A CMP (Chemical Mechanical Polishing) apparatus has been used in fabrication processes of a semiconductor integrated circuit device. The CMP apparatus typically includes a holding mechanism for holding a semiconductor wafer (an object to be polished), and a rotatable table with a polishing pad or fixed abrasive attached thereto. The apparatus of this type is operable such that the holding mechanism presses the semiconductor wafer against a polishing surface of the polishing pad or fixed abrasive on the rotating table, while supplying a polishing liquid, e.g., slurry, onto the polishing surface. The semiconductor wafer is polished by relative movement between the polishing pad or fixed abrasive and the semiconductor wafer.
When the polishing apparatus having the above-mentioned structures performs polishing of a semiconductor wafer, the surface of the polishing pad (or fixed abrasive) may be deformed due to frictional heat, or a polishing performance may be lowered due to a variation in polishing capability caused by a temperature distribution over the polishing surface of the polishing pad (or fixed abrasive). Therefore, it is necessary to cool the polishing surface so as to keep the polishing surface within a predetermined temperature range.
An example of a method of cooling the polishing surface is shown in FIG. 1. A cooling-medium passage 102 is provided in a table 101, so that a cooling medium, such as cooling water, flows through the cooling-medium passage 102 to thereby cool a polishing pad 103 attached to an upper surface of the table 101. Rotation of a shaft 104 causes the table 101 to rotate together with the polishing pad 103. During rotation of the polishing pad 103, a polishing liquid 106, such as slurry, is supplied from a supply nozzle 105 onto an upper surface of the polishing pad 103, and a substrate holding mechanism 107, such as a top ring, presses a semiconductor wafer 108 against the upper surface of the polishing pad 103 while rotating the semiconductor wafer 108. In this manner, the semiconductor wafer 108 is polished by relative movement (i.e., sliding contact) between the polishing pad 103 and the semiconductor wafer 108.
In the above-described polishing apparatus, friction between the semiconductor wafer 108 and the polishing pad 103 generates heat Q, which radiates as atmospheric radiant heat Q1, polishing-liquid radiant heat Q2, and cooling-medium radiant heat Q3. The atmospheric radiant heat Q1 is heat radiating from the surface of the polishing pad 103, the polishing-liquid radiant heat Q2 is heat radiating into the polishing liquid 106, and the cooling-medium radiant heat Q3 is heat radiating into the cooling medium in the cooling-medium passage 102. These heat radiations allow the polishing surface of the polishing pad 103 to maintain its temperature within a certain range. For example, experimental results confirmed that a surface temperature of the polishing pad 103 was 65° C. under conditions that the heat Q generated by polishing was 1900 W and an atmospheric temperature was 23° C. The heat Q radiated as the atmospheric radiant heat Q1 (=600 W), the polishing-liquid radiant heat Q2 (=600 W), and the cooling-medium radiant heat Q3 (=700 W). These results were obtained by measurements and calculations, which confirmed heat balance.
However, when the surface temperature of the polishing pad 103 is 65° C., efficient polishing may not be performed. To increase a polishing rate (removal rate), there is a need to lower the surface temperature of the polishing pad 103 to 45° C. Generally, heat release is proportional to a temperature difference. The temperature difference between the polishing-pad surface temperature 45° C. and the atmospheric temperature 23° C. is 22° C. In this case, the atmospheric radiant heat Q1 is 300 W, the polishing-liquid radiant heat Q2 is 300 W, the cooling-medium radiant heat Q3 is 350 W, and accordingly, the total heat (Q1+Q2+Q3) is 950 W. This means that an additional heat-radiation means is required in order to release the heat by nearly 1000 W.
One example of such a means for heat radiation is to provide the above-described cooling-medium passage 102 in the table 101. The polishing pad 103 on the upper surface of the table 101 is cooled by the cooling medium, e.g., cooling water, flowing through the cooling-medium passage 102. However, the polishing pad 103 typically uses a low heat conductive material, such as foamed urethane. Therefore, cooling from a back surface (lower surface) could not result in sufficient heat radiation from the front surface (upper surface), and it is difficult to lower the temperature to less than 65° C.
Japanese laid-open patent publication No. 11-347935 discloses another approach in which a jet of cooling gas, e.g., a cooled N2, is supplied from a nozzle to an upper surface of a polishing pad to cool it. This approach, however, has drawbacks for the following reasons. In this method, a jet of gas is supplied to the upper surface of the polishing pad, while polishing is performed. The jet of gas could dry the upper surface (i.e., polishing surface) to cause scratching of a surface of a workpiece due to compositions in a polishing liquid (e.g., slurry) or due to particles removed from the workpiece.
The aforementioned patent publication also discloses supply of a cooling liquid, e.g., pure water, from a nozzle onto the upper surface of the polishing pad to cool it. However, the cooling liquid would dilute the polishing liquid on the polishing surface of the polishing pad, causing a change in polishing conditions and unstable polishing rates.
The above patent publication further discloses providing a heat exchange member on the upper surface of the polishing pad so that a cooling medium is supplied from a supply device to the heat exchange member to directly cool the upper surface of the polishing pad. This method can effectively cool the upper surface of the polishing pad and can improve a cooling efficiency. However, since the heat exchange member is in direct contact with the upper surface of the polishing pad, the heat exchange member and the polishing pad could be worn.